A man holds a bookies information board marked with odds, besides the Houses of Parliament, in central London, Britain, April 18, 2017. [Photo/Agencies]

Critics of an early election accuse May of taking advantage of low ratings for the main opposition Labor Party. May has been insisting until days ago that she had no intention of calling an early election. Some opinion polls have put Labor more than 20 points behind the Conservatives.

May will be going into the election holding 330 of the 650 seats in the House of Commons, with a working majority of 17. The main opposition Labor Party has 229 seats, but many of the party's MPs are estranged from their leader Jeremy Corbyn.

May and her Brexit ministers face tough negotiations with Brussels to agree a deal for Britain after it leaves the EU.

In her speech on Tuesday at the door of 10 Downing Street, May made it clear why she wanted an early election.

She said: "At this moment of enormous national significance there should be unity in Westminster, but instead there is division. The country is coming together, but Westminster is not."

"Our opponents believe that because the government's majority is so small, our resolve will weaken and that they can force us to change course. They are wrong," she said.

There has been widespread public support for Monday's decision, while political experts have given mixed responses.

Professor Martin Smith, head of the University of York's Department of Politics, said: "With a large Conservative majority, the government will be able to get through any Brexit deal. Of course, there are going to be several difficulties for the Conservatives in the election campaign including the impact on Scotland and the potential for a second referendum, and a focus in the campaign on what sort of post-EU Britain the Conservatives want."